1. Field of the Invention
The present Invention generally relates to computer apparatus and, in a preferred embodiment thereof, more particularly relates to heat dissipation apparatus for computer microprocessors.
2. Description of Related Art
As computer microprocessors are provided with faster and faster clock speeds, the operating heat which these devices generate, and must be appropriately dissipated, correspondingly increases. The typical microprocessor used in a computer has a die portion (the microprocessor proper) which is exposed within a recessed area on the top side wall of the processor housing module (or xe2x80x9ccanxe2x80x9d) which is mounted on the computer""s system board.
The operating heat from this type of recessed processor die has heretofore been dissipated using a die cast metal heat sink screwed down to the top side of the processor housing module over the recessed die. In order to provide the requisite heat transfer interface between the bottom side of the heat sink and the top side of the recessed die it was necessary to place a layer of thermal grease between the top side of the die and the underside of the metal heat sink. As is well known, while thermal grease provides a good heat conduction path between the die and the heat sink, it is considered to be an undesirable interface material from a manufacturing standpoint because it tends to be quite messy and is easily spread beyond its originally intended location.
A potentially better interface material is a compliant thermal interface pad compressed between the bottom side of the heat sink and the top side of the die. However, in practice the use of such a compliant thermal Interface pad in lieu of thermal grease has not been practical with current high speed microprocessors of this general type due to two design criteriaxe2x80x94namely, bond line thickness and die pressure.
Bond line thickness refers to the variable height between the top side of the recessed die and the top side of the processor housing, the variation in the bond line thickness arising due to manufacturing tolerances. To compensate for this dimensional variance in bond line thickness, and to provide the necessary compression of a compliant thermal interface pad, the thermal interface pad must have a thickness that undesirably reduces the amount of die operating heat conducted therethrough. Specifically, the pad must have an initial undeformed thickness that extends from the top side surface of the recessed die to above the top side of the processor housing. Additionally, at least one manufacturer of high speed microprocessors of this type is now specifying a maximum pressure which may be exerted on the die. Thus, particularly when the bond line thickness is at the low end of its manufacturing tolerance level, the compression of a thermal interface pad against the die by the overlying, rigidly attached die cast heat sink can easily exceed this maximum design pressure.
Thus, the use of thermal grease as the heat transfer interface between the heat sink structure and the top side of the die has been the only technique that compensates for bond line thickness variations, while at the same time preventing excess pressure from being exerted by the heat dissipation apparatus on the recessed die and providing a satisfactory heat conduction path between the die and the heat sink secured to the top side of the processor housing. The bond line thickness variation from processor to processor, of course, makes it quite difficult to apply the correct amount of thermal grease to ensure that an efficient thermal interface is provided between the die and the overlying heat sink, while at the same time avoiding the attendant mess of placing too much grease in the die recess. As a practical matter, the amount of grease must be that which generally corresponds to the lowest die level within the housing recess (as determined by the manufacturer""s bond line thickness tolerance range). Thus, when the top side of the die is at the low end of the bond line thickness tolerance range (i.e., at its highest permissible point within the die recess), the applied quantity of thermal grease is more than Is needed. This undesirably aggravates the tendency of thermal grease to xe2x80x9cmigratexe2x80x9d and generally create a mess.
As can readily be seen from the foregoing, a need exists for an improved technique for dissipating operating heat from a recessed microprocessor die, of the type generally described above, without the previous necessity of using thermal grease as the heat transfer interface between the top side surface of the die and the heat dissipation apparatus overlying the die. It is to this need that the present invention is directed.
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, electronic apparatus having a heat-generating component is provided with specially designed heat dissipation apparatus operative to dissipate operating heat from a surface of the component. From a broad perspective, the heat dissipation apparatus includes a heat transfer structure having a portion movable in place thereof toward the surface: a heat sink member rotatably carried by the heat transfer structure portion, in thermal communication therewith, for movement in placed thereof therewith into heat-receiving proximity with the surface; and a force exerting structure operative to move the heat sink member into heat-receiving proximity with the surface.
The heat dissipation apparatus is illustratively incorporated in a computer system in the form of a portable notebook computer having a microprocessor and a data storage device operative to store data retrievable by the microprocessor. The microprocessor is the component with which the heat dissipation apparatus is operatively associated, and is of a type having a housing with an exterior wall having a recess formed therein, and a die portion inset within the recess and having a side surface from which the heat dissipation apparatus receives microprocessor operating heat.
In an illustrated preferred embodiment of the heat dissipation apparatus, the heat transfer structure includes a heat conductive support structure, representatively a sheet metal EMI shield wall, which overlies the processor housing die recess, and a thermosyphoning heat pipe. A condensing end portion of the heat pipe is flattened and is anchored to the underside of the shield wall, in a heat transfer relationship therewith, while the evaporating end of the heat pipe has a circular cross-section, overlies the die recess and is resiliently deflectable toward the side surface of the die. The flattening of the condensing portion of the heat pipe improves heat transfer from the heat pipe to the shield wall. While the condensing portion of the heat pipe is representatively placed in thermal communication with the shield wall, it could alternatively be placed in thermal communication with another heat-receiving structure such as, for example, a portion of the computer chassis.
The heat sink member is preferably secured to the evaporating end of the heat pipe for rotation relative thereto, and has a flat side which faces a thermal interface pad placed on the side surface of the die, and an opposite arcuate side. When the heat pipe evaporating end portion is resiliently deflected toward the die, the flat side of the heat sink member Is pressed against the outer side surface of the thermal interface pad.
The force exerting structure is representatively a clamping structure carried by the microprocessor housing, and has a movable resilient spring plate member which may be clamped against the arcuate side surface of the heat sink member to move it into the die recess and resiliently clamp its flat side against the outer side of the thermal pad, thereby placing the heat sink member in operative heat-receiving proximity with the side surface of the die.
During operation of the microprocessor, die operating heat is transferred to the shield plate sequentially through the thermal pad, the heat sink member and the heat pipe. Operating heat received in this manner from the die is dissipated from the shield wall by a fan that flows air along the shield plate. Representatively, the microprocessor and the heat dissipation apparatus are disposed in the base housing of a portable notebook computer, and the fan operates to draw cooling air through the base housing, flow the air along opposite sides of the shield wall, and then discharge the heated air from the base housing.
The unique construction Of the heat dissipation apparatus permits it to be operatively associated with the die without the undesirable use of thermal grease as the interface between the die and the heat dissipation apparatus. Instead, a thermal pad is used as such interface. Due to the variable movement of the heat sink member into the die recess, and the resilient clamping of the heat sink member against the thermal pad, the thermal pad can be quite thin, and does not have to extend outwardly from the die recess in its uncompressed state. Accordingly, the thickness of thermal pad may be minimally sized in a manner such that the pad provides a highly efficient conductive path between the die and the heat sink member.
Because the heat sink member is deflectable a variable distance into the die recess to bring the heat sink member into resiliently clamped contact with the thermal pad therein, the heat dissipation apparatus automatically compensates for variations In the bond line distance of the microprocessor. Additionally, since the clamping structure resiliently clamps the heat sink member against the thermal interface pad, excessive pressure forces on the die may easily be avoided. The use of the resilient spring plate member facilitates the avoidance of the exertion of excess clamping pressure on the die.
The heat dissipation apparatus is self-adjusting in yet another manner due to the rotatable mounting of the heat sink member on the resiliently deflectable heat pipe evaporating end portion, and the configuration of the heat sink member. Specifically, in the event that the flat bottom side of the heat sink member is not precisely parallel to the top side of the die before the clamping structure is used to press the heat sink member against the thermal pad, the subsequent resilient downward force of the spring plate member on the curved upper side of the heat sink member will automatically pivot the heat sink member about the heat pipe evaporating end portion, when the bottom side of the heat sink member initially contacts the thermal pad, in a manner such that the flat bottom side of the heat sink member bears against the thermal pad in a precisely parallel relationship with the top side of the heat-generating processor die.
While the heat dissipation apparatus of the present invention is representatively utilized in conjunction with a recessed processor die, it could also be utilized to advantage in a wide variety of other heat dissipation applications as well, and is not in any manner limited to removing operating heat from a recessed processor die.